Dynamic configuration of a flexible orthogonal frequency division multiplexing PHY transport data frame preamble

ABSTRACT

A method for operating a transmitting device to communicate with a receiving device is described herein. The method includes the step of the transmitting device selecting a root index value from a set of root index values. The method further includes the step of the transmitting device generating a frequency domain Constant Amplitude Zero Auto-Correlation sequence based on the selected root index value. The method further includes the step of the transmitting device modulating the Constant Amplitude Zero Auto-Correlation sequence by a pseudo-noise sequence. The method further includes the step of the transmitting device generating an Orthogonal Frequency Division Multiplexing symbol, wherein the frequency domain Constant Amplitude Zero Auto-Correlation sequence modulated by the pseudo-noise sequence defines subcarrier values for the Orthogonal Frequency Division Multiplexing symbol. The method further includes the step of the transmitting device transmitting the Orthogonal Frequency Division Multiplexing symbol as an initial Orthogonal Frequency Division Multiplexing symbol of a preamble of a frame to the receiving device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) from U.S. PatentApplication No. 62/041,478 filed on Aug. 25, 2014, which is incorporatedby reference herein in its entirety.

FIELD OF DISCLOSURE

The present disclosure relates to the field of wireless communication,and more particularly, to mechanisms for dynamically constructingOrthogonal Frequency Division Multiplexing (“OFDM”) physical transportframe preambles, to enable robust signal detection and service discoveryin broadcast networks.

BACKGROUND

In today's world, many electronic devices rely upon wirelessconnectivity for the reception of data from other connected devices. Ina typical wireless deployment, there may be one or more wireless accesspoints that transmit data, and one or more devices that receive datafrom the wireless access point(s).

In such a scenario, different devices may have different propagationchannel characteristics, and these may affect their wireless datareception from the same wireless access point. For example, a devicethat is near the wireless access point and/or that has a fixed location(or is slowly moving) may have better propagation channel conditionsthan would a device that is moving at a high velocity and/or that isfurther away from the wireless access point. The first device may fallinto a group of devices that can receive data encoded and transmittedwith one set of parameters (such as a high Forward Error Correction(FEC) code rate, a high modulation level, and/or a smaller subcarrierspacing in an Orthogonal Frequency Division Multiplexing (hereinafterreferred to as “OFDM”) system, while the second device may fall into agroup of devices that need data to be encoded and transmitted with asecond set of parameters (such as a low FEC code rate, a low modulationlevel, and/or a wider subcarrier spacing in an OFDM system).

There are many scenarios where a large number of devices may all wish toreceive identical data from a common source. One such example isbroadcast television, where a large number of television sets in varioushomes all receive a common broadcast signal conveying a program ofinterest. In such scenarios, it is significantly more efficient tobroadcast or multicast the data to such devices rather than individuallysignaling the same data to each device. However, programs with differentquality levels (e.g. high definition video, standard definition video,etc.) may need to be transmitted to different groups of devices withdifferent propagation channel characteristics. In other scenarios, itmay be desirable to transmit device-specific data to a particulardevice, and the parameters used to encode and transmit that data maydepend upon the device's location and/or propagation channel conditions.

As described above, different sets of transmitted data may need to betransmitted with different encoding and transmission parameters, eithersimultaneously or in a time-multiplexed fashion (or both). The amount ofdata to be transmitted in a particular data set and/or the encoding andtransmission parameters for that data set may vary with time.

At the same time, the demand for high-speed wireless data continues toincrease, and it is desirable to make the most efficient use possible ofthe available wireless resources (such as a certain portion of thewireless spectrum) on a potentially time-varying basis.

SUMMARY

A method for operating a transmitting device to communicate with areceiving device is described herein. The method includes the step ofthe transmitting device selecting a root index value from a set of rootindex values. The method further includes the step of the transmittingdevice generating a frequency domain Constant Amplitude ZeroAuto-Correlation sequence based on the selected root index value. Themethod further includes the step of the transmitting device modulatingthe Constant Amplitude Zero Auto-Correlation sequence by a pseudo-noisesequence. The method further includes the step of the transmittingdevice generating an Orthogonal Frequency Division Multiplexing symbol,wherein the frequency domain Constant Amplitude Zero Auto-Correlationsequence modulated by the pseudo-noise sequence defines subcarriervalues for the Orthogonal Frequency Division Multiplexing symbol. Themethod further includes the step of the transmitting device transmittingthe Orthogonal Frequency Division Multiplexing symbol as an initialOrthogonal Frequency Division Multiplexing symbol of a preamble of aframe to the receiving device.

A method for operating a receiving device to communicate with atransmitting device is described herein. The method includes the step ofthe receiving device receiving a set of samples of a signal transmittedby the transmitter. The method further includes the step of thereceiving device correlating the sample set against each of a pluralityof Constant Amplitude Zero Auto-Correlation sequences modulated bypseudo-noise sequences to detect an initial Orthogonal FrequencyDivision Multiplexing symbol of a preamble of a frame of the transmittedsignal, wherein the Constant Amplitude Zero Auto-Correlation sequencescorrespond respectively to distinct root index values and the pseudonoise sequences are based on pseudo-noise seed values. The methodfurther includes the step of the receiving device synchronizing anacquisition of symbol data sets corresponding to subsequent OrthogonalFrequency Division Multiplexing symbols of the preamble, wherein thesynchronizing of acquisition is based on a correlation peak associatedwith a particular Constant Amplitude Zero Auto-Correlation sequence thatgives a maximal correlation response among the plurality of ConstantAmplitude Zero Auto-Correlation sequences.

A method for communicating between a transmitting device and a receivingdevice is described herein. The method includes the step of atransmitting device generating a sequence of Orthogonal FrequencyDivision Multiplexing symbols for a preamble of a frame, includinggenerating an initial Orthogonal Frequency Division Multiplexing symbolof the sequence. Subcarrier values of the initial Orthogonal FrequencyDivision Multiplexing symbol are determined based on a ConstantAmplitude Zero Auto-Correlation sequence modulated by an initial portionof a pseudo-noise sequence. The step of the transmitting devicegenerating a sequence of Orthogonal Frequency Division Multiplexingsymbols further includes generating a plurality of Orthogonal FrequencyDivision Multiplexing symbols after the initial Orthogonal FrequencyDivision Multiplexing symbol. This includes determining subcarriervalues for the Orthogonal Frequency Division Multiplexing symbol basedon the Constant Amplitude Zero Auto-Correlation sequence modulated by acorresponding non-initial portion of the pseudo-noise sequence; applyinga corresponding cyclic shift to the subcarrier values for the OrthogonalFrequency Division Multiplexing symbol; and inverse transforming thesubcarrier values to obtain time domain samples for the OrthogonalFrequency Division Multiplexing symbol. The method further includes thestep of the transmitting device transmitting the sequence of OrthogonalFrequency Division Multiplexing symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, structures are illustrated that, togetherwith the detailed description provided below, describe exemplaryembodiments of the claimed invention. Like elements are identified withthe same reference numerals. It should be understood that elements shownas a single component may be replaced with multiple components, andelements shown as multiple components may be replaced with a singlecomponent. The drawings are not to scale and the proportion of certainelements may be exaggerated for the purpose of illustration.

FIG. 1 illustrates an example broadcast network.

FIG. 2 illustrate an example broadcast frame.

FIG. 3 illustrates example broadcast frame dimensions.

FIG. 4 is an example system for originating an example frame controlchannel.

FIGS. 5A-5B, respectively, illustrate example frame controlcompositions.

FIG. 6 illustrates an example PN sequence generator.

FIG. 7 illustrates example frame control subcarrier mapping.

FIG. 8 illustrates example field termination signaling.

FIG. 9 illustrates an example frame including partitions.

FIG. 10 an example method for operating a transmitting device.

FIG. 11 illustrates an example method for operating a receiving device.

DETAILED DESCRIPTION

Described herein is an extensible PHY layer signaling framework, and inparticular an associated preamble signal design to enable robustdetection and service discovery, system synchronization, and receiverconfiguration. The PHY relies on a preamble sent as an integral part ofevery transmit frame to allow for sync/detection and systemconfiguration. As will be described, the preamble design includes aflexible signaling approach to convey frame configuration and contentcontrol information to the broadcast receiver. The signal designdescribes the mechanism by which signal parameters are modulated on thephysical medium. The signaling protocol describes the specific encodingused to communicate parameter selections governing the transmit frameconfiguration. This enables reliable service discovery while providingextensibility to accommodate evolving signaling needs from a commonframe structure. Specifically, the design of the preamble enablesuniversal signal discovery independent of channel bandwidth. Thepreamble also enables reliable detection in the presence of a variety ofchannel impairments such as time dispersion and multipath fading,Doppler shift, and carrier frequency offset. In addition, multipleservice contexts are accessible based on mode detection during signaldiscovery enabling broad flexibility in system configuration. Thepreamble also facilitates extensibility to accommodate ongoing evolutionin service capability based on hierarchical signaling structure.Moreover, reusable bit-fields interpreted based on the detected servicemode/type enable bit-efficient signaling despite the level ofextensibility afforded.

FIG. 1 illustrates an example broadcast network 100 that uses theexample preamble design described herein. The broadcast network 100 mayinclude a plurality of base stations 101 a, 101 b . . . 101 n,illustratively suggested by base stations BS₁, BS₂, . . . , BS_(N)(hereinafter referred to as base stations 101). A broadcast gateway(“BG”) 102 may couple to the base stations 101 through any of a varietyof communication media. For example, in one embodiment, the broadcastgateway 102 may couple to the base stations 101 via the Internet, ormore generally, via a computer network. Each base station 101 wirelesslytransmits information to one or more user devices 103. (Each user deviceUD is denoted by a solid block circle.) Some of the user devices 103 maybe fixed devices such as televisions and desktop computers. Other onesof the user devices 103 may be nomadic devices such as tablet computersor laptop computers. Other ones of the user devices 103 may be mobiledevices such as mobile phones, automobile-based devices, aircraft-baseddevices, etc.

An operator (“Op) 104 of the broadcast network 100 may access thebroadcast gateway 102 (e.g., via the Internet), and provide networkconfiguration or operating instructions to the gateway 102. For example,the operator 104 may provide information such as one or more of thefollowing items: an expected distribution of user device mobility forone or more of the base stations; the cell size of one or more of thebase stations; a selection of whether the broadcast network or a subsetof the network is to be operated as a single frequency network (SFN) ora multi-frequency network (MFN); a specification of how differentservices (e.g., television content streams) are to be assigned todifferent types of user devices; and identification of portions ofbandwidth the broadcast network will not be using over correspondingperiods of time.

The broadcast gateway 102 may determine transmission control informationfor one or more base stations 101 of the broadcast network 100 based onthe network configuration or operating instructions. For a given basestation, the broadcast gateway 102 may determine: transmission samplerate; number of partitions; sizes of the partitions; FFT size and cyclicprefix size for each partition. The broadcast gateway 102 may send thetransmission control information to the base stations 101 so the basestations 101 may construct and transmit frames according to thetransmission control information. In other embodiments, the gateway 102may itself generate frames to be transmitted by each gateway 102 andsend the frames to the base stations 101. In yet other embodiments, thegateway 102 may generate low level instructions (e.g., physical layerinstructions) for the construction of frames to the base stations 101,and send those instructions to the base stations 101, which may simplygenerate frames based on the instructions.

Frame Structure

FIG. 2 illustrates an example broadcast frame 200. The frame 200occupies a specified duration independent of the underlying frameconfiguration to facilitate coordination with surrounding wirelesstransports. In this example, the frame 200 has a time duration of onesecond. However, it should be appreciated that the frame 200 may haveother suitable time durations. In one example, the frame length may bedynamically signaled. The broadcast frame 200 can be divided intopreamble 204 and payload 206 regions followed by an optional auxiliarytermination signal (ATS) field 208. In the example shown, the preamble204 and ATS 208 regions are indicated by the shaded areas at thebeginning and end of the frame 202. The relative lengths in time(horizontal axis) and numbers of symbols for each region are not shownto scale in this example diagram.

The preamble 204 can be further subdivided into frame control 210(hereinafter referred to as “PFCCH”) and content control 212 (hereinafter referred to as “PCCCH”) regions. Responsibilities of the tworegions can be summarized as follows. The PFCCH 210 is used to signalthe frame configuration to a receive terminal. It describes the signaldesign and the underlying signaling protocol. Frame configuration mayinclude a combination of one or more of the length of the preamble, thelength of the frame, the signal bandwidth and sampling rate, themodulation and coding applied to PCCCH 210, and the presence of ATS. ThePFCCH 210 further provides initial synchronization and establishes theframe operating mode. The PFCCH 210 also enables channel estimation andinitial carrier frequency offset (CFO) estimation.

The PCCCH 212 is used to signal payload configuration to the receiver.In particular, the PCCCH 212 describes the contents of the payloadregion including the number of partitions and the signal dimensions,such as the FFT size and CP duration, applied in each partition. ThePCCCH 212 also signals the mapping of data streams to each partitionincluding the modulation, coding scheme, and interleaver depth.

Detection of a particular preamble sets the context by which theremaining preamble symbols are interpreted. For example, use of thespectrum by a broadband service would map to a separate context signaledin the broadcast preamble as “private”. The broadband operator maychoose to define other fields to advertise to the broadcast users. Forexample, filed may define how long the transport will be occupied and inwhat signal bandwidth. The broadcast receiver is otherwise instructed toignore the present frame as belonging to a service context other thanthat which the broadcast device is equipped to receive.

It should be appreciated that in order for reliable detection in thepresence of a variety of channel impairments, certain servicerequirements may be necessary. For example, to lower the probability ofmissed detection (“MD”) and false alarm (“FA”) in additive whiteGaussian Noice (“AWGN”) and of multipath fading, a maximum Doppler shiftand delay spread tolerance may be imposed. In one example, the maximumDoppler shift given an FFT with 3 kHz sub-carrier spacing may be 288 MPH(463 KPH) @ 700 MHz or 96 MPH (154 KPH) @ 2100 MHz. In one example, thedelay spread tolerance may be 167 μs, or 31 MI (50 KM). It should beappreciated that Doppler tolerance can be increased for a given carrierfrequency by skipping subcarriers (i.e. inserting zeroes) at the samespacing to preserve signal bandwidth at the expense of detectionreliability and signaling capacity.

PFCCH

The PFCCH 210 provides a universal service entry point for the broadcastreceiver. It employs a fixed configuration known to all receive devices.In particular, the PFCCH 210 configuration may include a sampling rate,signal bandwidth, subcarrier spacing, and guard interval known to allreceive devices. The PFCCH 210 is initiated with a synchronizationsymbol positioned at the start of each frame period to enable servicediscovery, coarse synchronization and initial channel estimation.Parameters governing the frame structure including the symbolconfiguration used in PCCCH 212 are signaled in the remaining PFCCH 210symbol periods.

To minimize receiver complexity, PFCCH 210 may be sampled at a fixedfrequency. In one example, PFCCH may be sampled at 6.144 Ms/s. Thesignal is confined to a minimum bandwidth to enable reception by anyreceiver independent of the assigned channel bandwidth. In one example,the signal may be confined to a minimum 4.5 MHz bandwidth. FIG. 3illustrates example dimension 302 of a PFCCH 210. The FFT dimension 304is selected to ensure the required subcarrier spacing. A Cyclic Prefix(CP) 306 is inserted to ensure adequate delay spread tolerance betweenpreamble symbols. Thus, in the example illustrated:

$\begin{matrix}{{{B_{SIG} = {4.5\mspace{14mu}{MHz}}},{f_{S} = {6.144\mspace{14mu}{Ms}\text{/}s}}}{{{\Delta\; f} = {3\mspace{14mu}{kHz}}},{T_{GI} = {167\mspace{14mu}{µs}}}}{N_{FFT} = {\frac{f_{S}}{\Delta\; f} = 2048}}{N_{CP} = {{T_{GI} \cdot f_{S}} = 1024}}{T_{SYM} = {{\left( {N_{FFT} + N_{CP}} \right)/f_{s}} = {500\mspace{14mu}{µs}}}}} & {{Equ}\mspace{14mu}(1)}\end{matrix}$

FIG. 4 illustrates as system 400 for originating a PFCCH 210. A PFCCH210 originates with a Zadoff-Chu (“ZC”) sequence 402 modulated in thefrequency domain by a pseudo-noise (“PN”) sequence 404, with a sequencegenerator 410. The PN-sequence phase-rotates individual complexsubcarriers retaining the desirable Constant Amplitude ZeroAutocorrelation Waveform (“CAZAC”) properties of the originalZC-sequence, illustrated in FIG. 5A. The added phase rotation isintended to provide greater signal separation between cyclic shifts ofthe same root sequence suppressing spurious auto-correlation responsesobserved using a ZC-sequence without the addition of PN-sequencemodulation, illustrated in FIG. 5B.

The ZC constitutes a CAZAC sequence exhibiting excellent detectionproperties characterized by ideal cyclic autocorrelation. For example,the correlation with a cyclic shifted version of itself returns a deltafunction. The ZC-sequence is defined by a root, q, and cyclic shifts ofthe root sequence in the frequency domain producing a corresponding lagin the time domain.

$\begin{matrix}{{{a_{q}(n)} = e^{{- j}\;\pi\; q\frac{n{({n + 1})}}{N_{ZC}}}}{{{where}\mspace{14mu}{the}\mspace{14mu}{ZC}\mspace{14mu}{root}\mspace{14mu}{index}},{q \in \left\{ {1,\ldots\mspace{14mu},{N_{ZC} - 1}} \right\}},{n = 0},1,\ldots\mspace{14mu},{N_{ZC} - 1}}} & {{Equ}\mspace{14mu}(2)}\end{matrix}$

Cyclic shifts of the root sequence can be derived by replacing n in theabove equation Equ(2) with some value n-m, where m represents theintended time shift. The root sequence corresponds to m=0. The resultingsequence is computed as:

$\begin{matrix}{{{a_{q}\left( {n,m} \right)} = e^{{- j}\;\pi\; q\frac{{({n - m})}{({n - m + 1})}}{N_{ZC}}}}{{a_{q}\left( {n,m} \right)} = e^{{- j}\;\pi\; q\frac{({n^{2} - {2\;{mn}} + m^{2} + n})}{N_{ZC}}}}{{a_{q}\left( {n,m} \right)} = {{a_{q}\left( {n,0} \right)} \cdot e^{{- j}\;\pi\; q\frac{({m^{2} - {2\;{mn}}})}{N_{ZC}}}}}{{{{where}\mspace{14mu} q} \in \left\{ {1,\ldots\mspace{14mu},{N_{ZC} - 1}} \right\}},{n = 0},1,\ldots\mspace{14mu},{N_{ZC} - 1},{m\mspace{14mu}{represents}\mspace{14mu}{the}\mspace{14mu}{assigned}\mspace{14mu}{cyclic}\mspace{14mu}{shift}}}} & {{Equ}\mspace{14mu}(3)}\end{matrix}$

The PN-sequence serves in suppressing spurious off-peak responsesobserved in some sequence roots. The addition of a PN-sequence providesa reliable means to distinguish the initial symbol intended for syncdetection from subsequent symbols in the PFCCH 210. The naturalprogression of the PN-sequence, reset at the start of the preamble,eliminates the potential for correlation with delayed replicas of thesync detect symbol. It also minimizes the possibility of false detectionin the event the initial preamble symbol is missed due to burst noise,shadowing, or a deep channel fade.

FIG. 6 illustrates an example sequence generator 410. The PN-sequencegenerator 410 is derived from a Linear Feedback Shift Register (LFSR)602. Its operation is governed by a generator polynomial 604 specifyingthe taps in the LFSR feedback path followed by a mask 606 specifying theelements that contribute to the sequence output 608. Specification ofthe generator polynomial, mask and initial state of the registersrepresent a seed. For example a seed=f(g, m, r_(init)).

Referring again to FIG. 4, the system 400 includes a sub-carrier mappingmodule 412 for mapping output of the sequence generator 410 to theInverse Fast Fourier Transform (“IFFT”) 408 input. A CP module 406 isconfigured to add a CP to the IFFT 408 output.

In one example, the PN sequence is mapped to Quadrature Phase ShiftKeying (“QPSK”) symbols providing {±π/4, ±3π/4} rotations per subcarrierrelative to the root ZC sequence at the IFFT 408 input modulating thereal and imaginary signal components (i.e. I, Q) independently. In oneexample, Binary Phase-shift Keying (“BPSK”) modulation can be used aswell, providing {0,π} rotations with presumably less separation giventhat I and Q-signals are no longer modulated independently.

A PFCCH symbol 210 is configured to maximize use of the available signalbandwidth. The subcarrier mapping is additionally constrained to permituse of a prime-length ZC sequence. Therefore:

$\begin{matrix}{{N_{SC} = {{\left\lfloor \frac{B_{SIG}}{\Delta\; f} \right\rfloor - {1({null})}} = 1499}}{{N_{ZC} = {\max\left\lbrack {1\text{:}\mspace{14mu} N_{SC}} \right\rbrack}},{N_{ZC} \in {\mathbb{N}}_{P}}}} & {{Equ}\mspace{14mu}(4)}\end{matrix}$

The outputs of the complex sequence generator 410 are mapped by thesub-carrier mapping module 412 to the IFFT 408 input on either side ofthe DC subcarrier. Given an odd length sequence, one additionalsubcarrier is mapped to the negative frequencies such that an equalnumber of subcarriers are mapped to negative and positive frequencieswhere positive frequencies include DC.

The IFFT 408 output is cyclically extended by the CP module 406 toaccount for channel delay spread. The CP length is selected to exceedthe maximum expected delay spread tolerance. Thus:

$\begin{matrix}{T_{CP} = {\frac{N_{CP}}{f_{S}} = {167\mspace{14mu}{µs}}}} & {{Equ}\mspace{14mu}(5)}\end{matrix}$

FIG. 7 illustrates an example progression through PFCCH 410 symbolcontents to the PCCCH 412 contents of preamble 204. The firsttransmitted PFCCH symbol 708 provides sync detection and mode selection.It is also used for channel estimation. In one example, Sync detectionis based on correlation to one of many prescribed roots of the ZCsequence (zero cyclic shift). In one example, the detected rootsequence, including PN-modulation, determines the service type/modecarried in the frame. For example, service type/mode may include ONEMedia Standalone Transmission, ONE Media Transmission underconfiguration control of a Broadcast Management Exchange (BMX), ONEMedia BMX Beacon, Private Use, or another suitable service type/mode.The root sequence might additionally identify separate service classes,operating modes, transmitters/service operators, and so on.

In one example, channel estimation is performed at the receiver based oncross correlation with a local copy of the detected root sequence,including PN-modulation. The channel estimate is used in compensatingfor channel effects, time dispersion in particular, prior to decodingthe remaining PCCCH symbols 412.

Cyclic shifts of the detected root sequence are applied in symbols 710following initial sync detection, i.e. secondary symbol periods, toconvey the frame configuration. In one example, observed or estimatedcyclic shift is mapped to an assigned bit-field, the meaning of which isspecific to a current symbol period, such as proximity to the syncdetect symbol, interpreted relative to the context set by the detectedservice mode.

In one example, the interpretation in a secondary symbol period mightadditionally depend on the context set in a preceding symbol period. Forinstance, the transmitter might sub-divide the permissible cyclic shiftsin a given symbol period to establish separate contexts therebyextending the signaling hierarchy to multiple levels below the detectedservice type.

In one example, parameters signaled in the secondary symbol periods mayinclude one or more of frame count, frame duration, signal bandwidthemployed in PCCCH as well as the frame payload, the PCCCH FFT size andCP length, the PCCCH modulation, and code rate.

In one example, delayed correlation with the CP is computed persecondary symbol to refine frequency offset estimates, compensation forwhich is applied in the next symbol period.

As illustrated in FIG. 9, the sequence transmitted in the final symbolperiod is inverted (i.e. rotated 180°) signaling the end of PFCCH 410.In one example, the final PFCCH 410 symbol includes a cyclic shift asneeded to convey parameter selection as described above. In one example,inverting the phase of the sequence provides an efficient means toindicate the start of PCCCH 412 in the next symbol period whilepermitting the length of PFCCH 410 to be extended to increase signalingcapacity as needed.

PCCCH

The PCCCH 412 contains information necessary for a terminal to decodethe frame payload and extract portions or programs of interest. In oneexample, the PCCCH 412 includes the number of frame partitions.

In one example, the PCCCH 412 includes, for each partition, physicalresources allocated to that partition. This may include the number ofOFDM symbols allocated to that partition, as well as which particularsymbols are allocated to that partition. It should be appreciated thatdistinct partition may be interleaved with each other. The PCCCH 412 mayalso include, for each partition, FFT size and Cyclic prefix length. Inone example, the PCCCH 412 may also include the number of partitions inthe frame.

In one example, the PCCCH 412 includes, for each service data stream,service associated with that stream, physical resources allocated tothat stream, modulation used for that stream, and transport block sizein bytes.

In one example, the PCCCH 412 includes the presence/absence of anAuxiliary Termination Symbol (ATS) used to allow for transmitter ID,position/location information, discontinuous reception, and so on.

It should be appreciated that PCCCH is carried using conventional OFDMsymbols, the bandwidth, FFT size, and CP length of which are set inaccordance with the parameter settings communicated as part of PFCCH.

The modulation, code rate, and pilot density are also set according toparameters sent in PFCCH. The intent is to provision signaling in amanner that just exceeds the reliability of the payload symbols. Forexample, there is no benefit in using QPSK with a very low code rate forsignaling given a frame that contains a 256-QAM payload sent with arelatively high code rate (i.e. minimal redundancy). Instead, higherorder modulation and a higher code rate are used for signaling as wellto minimize overhead.

In one example, partitioning PCCCH is introduced to account for thepotential to encounter different channel conditions, potentially fordifferent service deployments. Different channel conditions may include,for example, mobile vs. fixed as well as the possibility of mixingmobile and fixed in the same transport.

FIG. 9 illustrates an example frame 900 including the PFCCH 210 and thePCCCH 212 divided into partitions 902. Reception under slow mobility,such as pedestrian speeds, is plagued by flat fading characterized bysignificant signal attenuation across all frequencies for brief periodsof time. A deep fade can last tens of microseconds (μs) compromisingdata integrity for whole symbol periods regardless of the assignedmodulation order and code rate. The data loss has potential to affectsignaling as well as data reception. PFCCH 210 benefits from substantialsignal processing gain providing robustness at SNR levels well below therequirements for payload data reception. On the other hand, PCCCH 212 iscloser in composition to the frame payload making it equally vulnerableto this kind of fading. Thus, dividing PCCCH 212 into partitions 902enables different methods of encoding to address different deploymentscenarios.

It should be appreciated that, in one example, partitioning as signaledin PFCCH improves time diversity increasing the reliability of PCCCHreception.

In one example, benign channels (Fixed/Ricean) employ one method ofCoding, Modulation, and Time Diversity and pedestrian channels(Raleigh/Flat Fading) would employ an alternate method of Coding,Modulation, and Time Diversity.

In one example, a scheduler is responsible for provisioning.

In one example, the encoding shows a signal that is compact in time andspans the centermost frequencies of the band. This kind of signaling maybe well suited for fixed reception where the potential to encounter flatfading is nearly non-existent. In another example, an alternate encodingmay spread the signal over a larger number of symbol periods occupyingresources placed at the band edges, perhaps alternating per symbolperiod for additional frequency diversity. This arrangement may bebetter suited for mobile reception where multiple symbol periods may becompromised due to flat fading. The likelihood of signal recovery may begreatly improved given the added time and frequency diversity.

Given the manner in which the two encodings are separated in frequency,the possibility exists to send both signal encodings at the same time,once in a manner best suited for fixed reception and once in a mannerbest suited for mobile reception. In one example, the contents of thefixed signaling method might be limited to that needed by the fixedreceiver, such as which frame partition(s) to monitor and theperiodicity of the corresponding payload symbols. Likewise, the contentsof the mobile signaling method may be restricted to the partitions andsymbol periods corresponding to the mobile service.

FIG. 10 illustrates an example method for operating a transmittingdevice. At step 1002, a transmitting device selects a root index valuefrom a set of index values. At step 1004, the transmitting devicegenerates a frequency domain CAZAC sequence based on the selected rootindex value. At step 1006, the transmitting device modulates the CAZACsequence by a PN sequence. At step 1008, the transmitting devicegenerates a OFDM symbol defined by the CAZAC sequence modulated by thePN sequence. At step 1010, the transmitting device transmits the OFDMsymbol as an initial OFDM symbol of a preamble.

FIG. 11 illustrates an example method for operating a receiving device.At step 1102, a receiving device receives a set of samples of a signaltransmitted by the transmitter. At step 1104, the receiving devicecorrelates the sample set against each of a plurality of CAZAC sequencesmodulated by P-N sequences to detect an initial OFDM symbol of apreamble of a frame of the transmitted signal, wherein the CAZACsequences correspond respectively to distinct root index values and theP-N sequences are based on P-N seed values. At step 1106, the receivingdevice synchronizes an acquisition of symbol data sets corresponding tosubsequent OFDM symbols of the preamble, wherein the synchronizing ofacquisition is based on a correlation peak associated with a particularCAZAC sequence that gives a maximal correlation response among theplurality of CAZAC sequences.

Any of the various embodiments described herein may be realized in anyof various forms, e.g., as a computer-implemented method, as acomputer-readable memory medium, as a computer system, etc. A system maybe realized by one or more custom-designed hardware devices such asApplication Specific Integrated Circuits (ASICs), by one or moreprogrammable hardware elements such as Field Programmable Gate Arrays(FPGAs), by one or more processors executing stored programinstructions, or by any combination of the foregoing.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of the methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a computer system may be configured to include aprocessor (or a set of processors) and a memory medium, where the memorymedium stores program instructions, where the processor is configured toread and execute the program instructions from the memory medium, wherethe program instructions are executable to implement any of the variousmethod embodiments described herein (or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets). Thecomputer system may be realized in any of various forms. For example,the computer system may be a personal computer (in any of its variousrealizations), a workstation, a computer on a card, anapplication-specific computer in a box, a server computer, a clientcomputer, a hand-held device, a mobile device, a wearable computer, asensing device, a television, a video acquisition device, a computerembedded in a living organism, etc. The computer system may include oneor more display devices. Any of the various computational resultsdisclosed herein may be displayed via a display device or otherwisepresented as output via a user interface device.

To the extent that the term “includes” or “including” is used in thespecification or the claims, it is intended to be inclusive in a mannersimilar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed (e.g., A or B) it is intended to mean “Aor B or both.” When the applicants intend to indicate “only A or B butnot both” then the term “only A or B but not both” will be employed.Thus, use of the term “or” herein is the inclusive, and not theexclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into”are used in the specification or the claims, it is intended toadditionally mean “on” or “onto.” Furthermore, to the extent the term“connect” is used in the specification or claims, it is intended to meannot only “directly connected to,” but also “indirectly connected to”such as connected through another component or components.

While the present application has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the application, in its broaderaspects, is not limited to the specific details, the representativeapparatus and method, and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the spirit or scope of the applicant's general inventive concept.

What is claimed is:
 1. A method for operating a transmitting device tocommunicate with a receiving device, the method comprising: thetransmitting device selecting a root index value from a set of rootindex values; the transmitting device generating a frequency domainConstant Amplitude Zero Auto-Correlation (CAZAC) sequence based on theselected root index value; the transmitting device modulating thefrequency domain CAZAC sequence by a pseudo-noise (PN) sequence togenerate a complex sequence; the transmitting device generating anOrthogonal Frequency Division Multiplexing (OFDM) symbol by mapping thecomplex sequence to a plurality of subcarriers; the transmitting devicetransmitting the OFDM symbol as an initial OFDM symbol of a preamble ofa frame to the receiving device; and the transmitting device generatingsubsequent OFDM symbols of the preamble, the generating of subsequentOFDM symbols of the preamble comprising: applying respective cyclicshifts to the frequency domain CAZAC sequence, wherein each of therespective cyclic shifts is selected from a set of cyclic shifts basedon respective frame configuration information; and transmitting thesubsequent OFDM symbols in the preamble of the frame.
 2. The method ofclaim 1, wherein the initial OFDM symbol comprises a frame controlsymbol configured to provide initial synchronization.
 3. The method ofclaim 1, wherein the frequency domain CAZAC sequence includes aZadoff-Chu (ZC) sequence.
 4. The method of claim 1, wherein thefrequency domain CAZAC sequence indicates a service type provided by theframe, from a set of service types.
 5. The method of claim 1, whereinthe subsequent OFDM symbols in the preamble of the frame comprisecontent control symbols configured to describe contents of the frame. 6.The method of claim 1, further comprising the transmitting deviceapplying a phase inversion operation to at least one of the subsequentOFDM symbols prior to transmitting the subsequent OFDM symbols.
 7. Themethod of claim 1, wherein frame configuration information signaled byan OFDM symbol of the subsequent OFDM symbols is based on prior frameconfiguration information signaled by a prior OFDM symbol of thesubsequent OFDM symbols, the OFDM symbol being after the prior OFDMsymbol among the subsequent OFDM symbols.
 8. A method for operating areceiving device to communicate with a transmitting device, the methodcomprising: the receiving device receiving a set of samples of a signaltransmitted by the transmitting device; the receiving device correlatingthe set of samples against each of a plurality of Constant AmplitudeZero Auto-Correlation (CAZAC) sequences modulated by pseudo-noise (PN)sequences to detect an initial Orthogonal Frequency DivisionMultiplexing (OFDM) symbol of a preamble of a frame of the transmittedsignal, wherein the CAZAC sequences correspond respectively to distinctroot index values and the PN sequences are based on PN seed values; thereceiving device identifying a particular CAZAC sequence from among theplurality of CAZAC sequences, the particular CAZAC sequencecorresponding to a maximal correlation response; and the receivingdevice obtaining subsequent OFDM symbols of the preamble based on theparticular CAZAC sequence, wherein the subsequent OFDM symbols includesymbol data sets.
 9. The method of claim 8, wherein the plurality ofCAZAC sequences each includes a Zadoff-Chu sequence.
 10. The method ofclaim 8, wherein the particular CAZAC sequence indicates a service typefor the frame.
 11. The method of claim 8, further comprising thereceiving device, for each of the symbol data sets, determining acorresponding cyclic shift relative to the particular CAZAC sequence,wherein corresponding frame configuration information is based at leastin part on the corresponding cyclic shift and the particular CAZACsequence.
 12. The method of claim 8, wherein frame configurationinformation signaled by an OFDM symbol of the subsequent OFDM symbols isbased on prior frame configuration information signaled by a prior OFDMsymbol of the subsequent OFDM symbols, the OFDM symbol being after theprior OFDM symbol among the subsequent OFDM symbols.
 13. A method forcommunicating between a transmitting device and a receiving device, themethod comprising: modulating a Constant Amplitude Zero Auto-Correlation(CAZAC) sequence by a pseudo-noise (PN) sequence to generate a complexsequence; mapping the complex sequence to a plurality of subcarriers togenerate first subcarrier values for an initial Orthogonal FrequencyDivision Multiplexing (OFDM) symbol; applying a cyclic shift to theCAZAC sequence to generate a cyclically shifted CAZAC sequence;modulating the cyclically shifted CAZAC sequence by the PN sequence togenerate a second complex sequence; mapping the second complex sequenceto the plurality of subcarriers to generate second subcarrier values fora subsequent OFDM symbol; and transmitting the initial and subsequentOFDM symbols in a frame preamble.
 14. The method of claim 13, furthercomprising generating the PN sequence using a linear feedback shiftregister.
 15. The method of claim 13, further comprising: inverting thesecond complex sequence when the subsequent OFDM symbol corresponds to alast OFDM symbol of the frame preamble.
 16. The method of claim 13,further comprising: applying an Inverse Fast Fourier Transform (IFFT) tothe first subcarrier values to generate the initial OFDM symbol.
 17. Atransmitting device, comprising: a memory storing program instructions;and a processor, upon executing the program instructions, configured to:select a root index value from a set of root index values; generate afrequency domain Constant Amplitude Zero Auto-Correlation (CAZAC)sequence based on the selected root index value; modulate the frequencydomain CAZAC sequence by a pseudo-noise (PN) sequence to generate acomplex sequence; map the complex sequence to a plurality of subcarriersto determine subcarrier values for an initial Orthogonal FrequencyDivision Multiplexing (OFDM) symbol of a frame preamble; apply a cyclicshift to the frequency domain CAZAC sequence to generate a cyclicallyshifted CAZAC sequence, wherein the cyclically shifted CAZAC sequence ismodulated by the PN sequence to generate a second complex sequence; andmap the second complex sequence to the plurality of subcarriers togenerate subsequent subcarrier values for a subsequent OFDM symbol ofthe frame preamble.
 18. The transmitting device of claim 17, wherein theroot index value includes a non-prime value.
 19. The transmitting deviceof claim 17, wherein the processor, upon executing the programinstructions, is further configured to: apply an Inverse Fast FourierTransform (IFFT) to the subcarrier values to generate the initial OFDMsymbol; and transmit the initial OFDM symbol to a receiving device. 20.The transmitting device of claim 17, wherein the frequency domain CAZACsequence includes a Zadoff-Chu (ZC) sequence.
 21. The transmittingdevice of claim 17, wherein the processor, upon executing theinstructions, is further configured to: invert the second complexsequence when the subsequent OFDM symbol corresponds to a last OFDMsymbol of the frame preamble.
 22. A method for enhancing detection of aninitial Orthogonal Frequency Division Multiplexing (OFDM) symbol of aframe preamble, comprising: generating a Zadoff-Chu (ZC) sequence usinga root index value selected from a set of root index values includingprime and non-prime root index values; modulating the ZC sequence by apseudo-noise (PN) sequence to generate a complex sequence; generatingthe initial OFDM symbol based on the complex sequence; transmitting theinitial OFDM symbol to a receiver in a first symbol period of the framepreamble; cyclically shifting the ZC sequence to generate a cyclicallyshifted ZC sequence; modulating the cyclically shifted ZC sequence bythe PN sequence to generate a second complex sequence; generating asubsequent OFDM symbol based on the second complex sequence; andtransmitting the subsequent OFDM symbol to the receiver in a secondsymbol period of the frame preamble adjacent to the first symbol period.